• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.4
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• pp.291-296
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• 2022

Capacitor is one of the reliability-critical components in power converters. The lifetime of the capacitor decreases as the operating temperature increases, and power losses caused by capacitor current are the main cause of the capacitor temperature increase. Therefore, various studies are being conducted to improve the lifetime of the capacitor by reducing the current of DC-link capacitors. In this study, pulse width modulation methods proposed for improving the lifetime of DC-link capacitors of the three-level NPC inverter are comparatively analyzed. The lifetime evaluation of the DC-link capacitor under different modulation methods is performed at component level first and then system level by considering all capacitors by applying Monte Carlo simulation. Furthermore, their effects on the efficiency and THD of the output current are also considered.

• International Journal of Computer Science & Network Security
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• v.22 no.8
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• pp.123-128
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• 2022

The main purpose of the study is to determine the features of the implementation of public authority in the context of modern international security challenges. The fact that public authority is a necessary regulator of the life of society ensures its development, unity, and manageability, which is an important factor in the organization and orderliness of society adds to the actualization of the research topic. The research methodology includes a set of theoretical methods of analysis. Based on the results of the study, key aspects of the implementation of public authority in the context of modern international security challenges were identified. The study has limitations, and they relate to the practical aspect of the implementation of public authority in the context of modern international security challenges.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09a
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• pp.177-178
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• 2006

The results of monotonic and cyclic uniaxial compression tests, in which the deviatoric component of the stress is predominant, carried out on green and recrystallized iron compacts with different levels of density are presented and discussed in order to analyse the macro and micro-mechanisms governing the mechanical behaviour of non-sintered PM materials. The plastic deformation of the particles, especially at the contact areas between neighbouring grains, produces an internal friction responsible for the main features observed in the behaviour of green metallic compacts. These results show important discrepancies with the plasticity models, Cam-Clay and Drucker-Prager Cap.

• Journal of the Korean Society for Precision Engineering
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• v.12 no.9
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• pp.59-65
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• 1995

The cam is used to a main component in a variety of automatic machines and instruments. To meet the demand of a complicated operation and of reducing weight for automatic machine, Curve Blending Technology, in which each of the basic curves suitable for individual interval is connected, is used for the cam design. In the curve blending, it is necessary to select appropriate elementary curve for each interval and to confirm the dynamic continuity at connecting points between adjoining elementary curves. This paper represented the elementary curve selection method to select an appropriate curve for each interval, and executed computation for the follower displacement and angular displacement of each interval. The paper made an analysis and examine closely for elementary curves to synthesizing curve blending, and it performed dynamic conditions clearly at every points on the cam motions. Therefore the curve blending technology presented by the paper turned into easier work.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.27 no.2
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• pp.146-159
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• 2023

This paper proposes a hybrid algorithm combining K-means clustering and watershed algorithms for flower segmentation and counting. We use the K-means clustering algorithm to obtain the main colors in a complex background according to the cluster centers and then take a color space transformation to extract pixel values for the hue, saturation, and value of flower color. Next, we apply the threshold segmentation technique to segment flowers precisely and obtain the binary image of flowers. Based on this, we take the Euclidean distance transformation to obtain the distance map and apply it to find the local maxima of the connected components. Afterward, the proposed algorithm adaptively determines a minimum distance between each peak and apply it to label connected components using the watershed segmentation with eight-connectivity. On a dataset of 30 images, the test results reveal that the proposed method is more efficient and precise for the counting of overlapped flowers ignoring the degree of overlap, number of overlap, and relatively irregular shape.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2020.11a
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• pp.46-47
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• 2020

Oyster shells and egg shells consist of CaCO3, which is known to have excellent fire performance as the main component, and research is currently being conducted as a fireproof board material. Therefore, in this study, the physical and chemical properties of oyster shell powder and egg shell powder are studied to find out the applicability of fireproof board

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.71.2-71.2
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• 2019

In order to gather clues to surface mineralogy of asteroids, we classify their taxonomy based on their reflected spectra. It is remarkable that a large number of asteroids plotted in the proper orbital element space with distinct colors according to their taxonomic types reveal the dynamical evolution and the structure in the near-Earth space, the main-belt and beyond. Although we have ~1×10⁶ known objects, no more than ~3×10³ of them are properly classified taxonomically as visible-near infrared spectroscopy is costly. On the other hand, multi-wavelength broadband photometry in the visible region provides a rather inexpensive alternative tool for approximate taxonomy. Thus we have conducted multi-band observations systematically using Korea Microlensing Telescope Network (KMTNet) with BVRI and griz filters since back in 2015. We then applied aperture photometry with elliptical apertures to fit the trails of objects during the exposures, and classified them with the principle component indices of Ivezic et al. (2001). We will make use of our new, three dimensional asteroid classification scheme for the next step.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2020.07a
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• pp.546-549
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• 2020

본 논문에서는 최신 비디오 코딩 기술에서 잔차(Residual)신호 변환을 효율적으로 수행하기 위한 부동기저(Basis)를 사용하는 방법을 제안한다. 기존의 DCT-II 나 DST-VII 과 같은 고정 기저를 사용하는 방법은 대부분의 잔차신호들에 대해 효과적으로 비상관화(decorrelation)를 수행하지만 복잡한 잔차 신호일수록 성능이 떨어지는 문제가 있었다. 이러한 압축 성능하락 문제를 줄이기 위하여 PCA(Principle Component Analysis) 방법 중 하나인 KLT(Karhunen-Loeve Transform)를 이용하여 부동(floating) 변환 기저를 유도하는 방법을 제안한다. 기존의 KLT 를 이용한 변환 커널 유도 방법들의 문제점인 부호화기 및 복호화기 계산 복잡도를 줄이기 위하여 KL 커널을 분해가능한(Separable) 2 개의 1 차원 커널로 유도하는 방법을 제안하고, 원본 잔차신호와 유사한 텍스처를 찾아 커널을 예측하는 과정을 간소화하는 방법을 제안한다. 제안하는 방법은 HEVC 에서 실험되었으며 정지영상 코딩 Main-Profile 에서 평균 1.4%가량의 BD-PSNR(Bjontegaard Delta-Peak Signal to Noise Ratio) 성능 향상을 보였으며 특히 스크린 컨텐츠 영상에서 최대 4.5%의 성능 향상을 보인다.

• Journal of the Korea Institute of Military Science and Technology
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• v.26 no.4
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• pp.361-370
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• 2023

Swarm has recently become a critical component of offensive and defensive systems. Multi-agent reinforcement learning(MARL) empowers swarm systems to handle a wide range of scenarios. However, the main challenge lies in MARL's scalability issue - as the number of agents increases, the performance of the learning decreases. In this study, transfer learning is applied to advanced MARL algorithm to resolve the scalability issue. Validation results show that the training efficiency has significantly improved, reducing computational time by 31 %.

• The Bulletin of The Korean Astronomical Society
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• v.46 no.2
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• pp.69.1-69.1
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• 2021

We present preliminary results of the VLA archival HI data of local AGN hosts. The sample consists of the galaxies selected from the Swift-BAT hard X-ray survey. The main goal is to probe the gas environment of the sample in order to verify the role of gas accretion as one of the major AGN triggering mechanisms. HI, as a mostly diffuse and extended gas component in many galaxies, is a sensitive tracer to explore the impact of the surroundings on galaxies. In this work, we therefore probe the HI imaging data of a subsample of BAT-BASS AGN hosts, starting with the cases for which relatively high HI fluxes have been reported from the past single-dish observations. Based on their resolved HI properties, we will discuss the possibility of gas accretion and its role in powering AGNs in these examples.